Fascinating study finds indigenous peoples in South America share genetics with those in Australia

During the last ice age, when hunters and gatherers crossed the ancient Bering Land Bridge that connected Asia with North America, they carried something special with them in their genetic code: pieces of ancestral Australian DNA, a new study finds on April 2. Over the generations, these people and their descendants trekked southward, making their way to South America. Even now, more than 15,000 years after these people crossed the Bering Land Bridge, their descendants — who still carry ancestral Australian genetic signatures — can be found in parts of the South American Pacific coast and in the Amazon, the researchers found. The new research builds on earlier work, first published in 2015, which showed that ancient and modern Indigenous people in the Amazon shared specific genetic signatures — known as the Ypikuéra, or Y signal — with modern-day Indigenous groups in South Asia, Australia and Melanesia, a group of islands in Oceania. This genetic connection caught many scientists off guard, and it remains "one of the most intriguing and poorly understood events in human history," the researchers wrote in the new study. To investigate the Y signal further, a team of scientists in Brazil and Spain dove into a large dataset containing the genetic data of 383 Indigenous people from different parts of South America. The team applied statistical methods to test whether any of the Native American populations had "excess" genetic similarity with a group they called the Australasians, or Indigenous peoples from Australia, Melanesia, New Guinea and the Andaman Islands in the Indian Ocean. In other words, the team was assessing whether a given Native American population shared significantly more genetic variants with Australasians than other Native Americans do. South American groups that did have more genetic similarities with Australasians were interpreted by the new researchers as being descendants of the first Americans and Australasian ancestors, who coupled together at least 15,000 years ago. As expected, the study confirmed the previous findings of Australasian genetic ties with the Karitiana and Suruí, Indigenous peoples in the Amazon. But the new genetic analysis also revealed a big surprise: The Australasian connection was also found in Peru's Chotuna people, an Indigenous group with ancestral ties to the Pacific Coast; the Guaraní Kaiowá, a group in central west Brazil; and the Xavánte, a group on the central Brazilian Plateau.